The present invention relates to an autostereoscopic display.
Autostereoscopic displays are well-known and examples of such displays are disclosed in EP 0 602 934, EP 0 656 555, EP 0 708 351, EP 0 726 482, EP 0 829 743, EP 0 833 183 (equivalent to GB 2 317 710) and EP 0 860 728. EP 0 829 744 discloses an example of such a display which is switchable between an autostereoscopic mode and a two dimensional mode. An autostereoscopic display capable of providing crosstalk correction for removing or reducing the effects of crosstalk between left eye and right eye images is disclosed in EP 0 953 962. Such displays may, for example, be based on liquid crystal spatial light modulators comprising arrays of picture elements (pixels) which modulate a light source in accordance with image data representing at least two homologous images.
EP 0 833 183 and GB 2 317 710 discloses a parallax barrier embodied by a liquid crystal device for switching between a barrier mode and a clear mode. The barrier is associated with a spatial light modulator of transmissive type to form an autostereoscopic display which can be switched to a two dimensional full resolution mode.
Transflective displays which are capable of operating selectively in a transmissive mode or a reflective mode are also known. An example of a transflective liquid crystal display is disclosed in M. Kubo et al, “Development of advanced TFT with good legibility under any intensity of ambient light”, Proceedings of Information Displays Workshop 1999, Sendai, Japan, pages 183 to 186.
FIG. 1 of the accompanying drawings illustrates a known type of display which is of the transmissive type and which may be operated in two dimensional (2D) and three dimensional (3D) modes. The display comprises a liquid crystal spatial light modulator (SLM) 1 providing an array of pixels such as 2. Colour filtering (not shown) is provided so that the pixels are arranged as groups of red, green and blue (RGB) pixels for displaying a full colour image. The pixels are also arranged as columns for displaying interleaved vertical strips of left (L) and right (R) images.
A backlight 3 is disposed behind the SLM 1 and directs light towards the SLM through a 2D/3D switching arrangement 4, a patterned retarder 5, and an input polariser 6 of the liquid crystal device (LCD) forming the SLM 1. Light transmitted through the SLM 1 passes through an output polariser 7.
In the 3D mode of operation, the switching arrangement 4 is configured as a polariser which supplies linearly polarised light to the patterned retarder 5. The retarder 5 comprises alternating region in the form of a first group of regions such as 8 which have no effect on the polarisation of the light passing therethrough and relatively narrow regions 9 which rotate the polarisation of the light passing therethrough by 90°. The polariser 6 is arranged to block light passing through the regions 8 and to transmit light passing through the regions 9 so that the combination of the retarder 5 and the polariser 6 forms a rear parallax barrier with slits corresponding to the regions 9.
The parallax barrier controls the direction of light passing through the pixels such that light passing through those pixels which display the left eye image forms a left eye viewing window at a predetermined viewing distance from the display whereas light passing through those pixels displaying a right eye image forms a right eye viewing window at the viewing distance.
When the display is switched to the 2D mode of operation, the switching arrangement 4 is arranged not to polarise the light from the backlight 3. The structure of the patterned retarder 5 is required to be invisible and light from the backlight 3 passes through the pixels in all directions to provide a wide viewing angle. The SLM 1 is controlled to display a 2D image.
FIG. 2 of the accompanying drawings illustrates a typical example of a transflective display which may be used in an autostereoscopic display of the type shown in FIG. 1. The display is based on a liquid crystal device having a liquid crystal layer 10 and red, green, and blue colour filters 11. A microreflective structure 12 is provided for the reflective mode of operation whereas a backlight 13 is provided for the transmissive mode of operation. Polarisers/retarders are provided as shown at 14 and 15.
When a transflective display, for example of the type shown in FIG. 2, is used in a rear parallax barrier autostereoscopic display, for example of the type shown in FIG. 1, the display may be used in the autostereoscopic mode only in the transmissive mode of the SLM. In particular, the left and right eye viewing windows are produced only by light transmitted from the backlight through the parallax barrier structure. However, in many viewing conditions, ambient light is reflected to the eyes of an observer from the display so that an observer sees a mixture of light transmitted from the backlight through the SLM and ambient light modulated by the SLM and reflected, for example, by the microreflective structure 12 shown in FIG. 2. Whereas transmitted light modulated by the left and right eye images is seen substantially only by the left and right eyes, respectively, of the observer, reflected light is seen by both eyes of the observer and this may contribute greatly to image crosstalk which degrades the 3D effect. For example, if the reflected brightness is 10% of the transmitted brightness, this adds approximately 10% of crosstalk. Thus, in order to provide the best 3D viewing conditions during the autostereoscopic 3D mode of operation, the brightness of the reflected ambient light should be small compared with the transmitted light. Conversely, when the reflected ambient light is excessive, the resulting image crosstalk greatly degrades the 3D effect to the point where 3D operation is ineffective. This may result in visual stress to the observer.